Binder composition for secondary battery, cathode and lithium battery including the binder composition

ABSTRACT

In an aspect, a binder composition for a secondary battery including a first fluoropolymer binder including a tetrafluoroethylene polymer binder, a second fluoropolymer binder including a vinylidene fluoride binder, and a non fluoropolymer binder is provided.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

Any and all priority claims identified in the Application Data Sheet, orany correction thereto, are hereby incorporated by reference under 37CFR 1.57. For example, this application claims priority to and thebenefit of Korean Patent Application No. 10-2014-0003602, filed on Jan.10, 2014, in the Korean Intellectual Property Office, the disclosure ofwhich is incorporated herein in its entirety by reference.

BACKGROUND

1. Field

One or more embodiments of the present disclosure relate to a bindercomposition for a secondary battery, and a cathode and a lithium batteryeach including the binder composition.

2. Description of the Related Technology

Lithium batteries are used in various applications due to their highvoltage and high energy density. For example, electric vehicles (HEV orPHEV) need to operate at high temperature, to be charged or dischargedwith a great amount of electricity, and to be used for a long period oftime. Accordingly, electric vehicles require lithium secondary batterieswith excellent energy density and lifespan characteristics.

To provide lithium batteries with high energy density and excellentlifespan characteristics, an increase in amounts of an electrode activematerial and a conductive agent and a decrease in an amount of a binder,in an electrode, are required. However, when the amount of the binderdecreases, dispersibility and binding force of the electrode activematerial and/or the conductive agent and flexibility of the electrodeactive material layer deteriorate. Accordingly, during charging anddischarging, the electrode active material may be separated from acurrent collector and thus, cyclic characteristics may deteriorate.Thus, a binder is required that, even in a small amount, providesdispersibility of electrode active material and/or conductive agent,binding force of an electrode plate, and flexibility of an electrodeplate, to an electrode.

For example, a fluoropolymer binder, such as a polar functionalgroup-free polyvinylidene fluoride, swells less with respect to anorganic electrolytic solution, and thus, when a battery operates, thebinder may contribute to retaining the structure of an electrode and anactive material may have improved dispersibility. However, such afluoropolymer binder shows poor properties in terms of dispersibility ofa conductive agent, binding force of an electrode plate, and flexibilityof an electrode plate.

A non fluoropolymer binder, such as a hydrogenatedacrylonitrile-butadiene binder, may have, compared to a fluoropolymerbinder, improved dispersibility of a conductive agent, improvedflexibility of an electrode plate, and improved binding force of anelectrode plate. However, the non fluoropolymer binder swells too muchwith respect to an electrolytic solution. Accordingly, the nonfluoropolymer binder is needed to be used in a restricted amount.

Thus, a binder is required that has improved binding force andflexibility at the same time to improve energy density and lifespancharacteristics of a lithium battery.

SUMMARY OF CERTAIN INVENTIVE ASPECTS

One or more embodiments of the present disclosure provide a bindercomposition for a secondary battery, having improved binding force andflexibility and a novel composition.

One or more embodiments of the present disclosure provide a cathodeincluding the binder composition.

One or more embodiments of the present disclosure provide a lithiumbattery including the cathode.

A binder composition for a secondary battery according to an embodimentof the present disclosure includes: a first fluoropolymer binderincluding a tetrafluoroethylene polymer binder; a second fluoropolymerbinder including a vinylidene fluoride binder; and a non fluoropolymerbinder including a repeating unit derived from an acryl monomer and arepeating unit derived from an olefin monomer.

A cathode according to an embodiment of the present disclosure includes:a cathode active material; a conductive agent; and the bindercomposition.

A lithium battery according to an embodiment of the present disclosureincludes the cathode.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of the embodiments, taken inconjunction with FIG. 1 which is a schematic view of a lithium batteryaccording to an embodiment of the present disclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments, examples of whichare illustrated in the accompanying drawings, wherein like referencenumerals refer to like elements throughout. In this regard, the presentembodiments may have different forms and should not be construed asbeing limited to the descriptions set forth herein. Accordingly, theembodiments are merely described below, by referring to the figures, toexplain aspects of the present description. Expressions such as “atleast one of,” when preceding a list of elements, modify the entire listof elements and do not modify the individual elements of the list.

Hereinafter, a binder composition for a secondary battery according toan embodiment of the present disclosure, a cathode including the bindercomposition, and a lithium battery including the cathode will bedescribed in detail.

When a typical binder for a secondary battery, such as a fluoropolymerbinder, is used, binding force of an electrode plate, flexibility of anelectrode plate, and dispersibility of a conductive agent decrease. Ithas surprisingly been found that when a tetrafluoroethylene polymerbinder and a non fluoropolymer binder including a repeating unit derivedfrom an acryl monomer and a repeating unit derived from an olefinmonomer are appropriately mixed with the vinylidene fluoride binder inpreparing a binder composition for a secondary battery, the preparedbinder provides flexibility of an electrode plate, binding force of anelectrode plate, and dispersibility of the conductive agent, leading tomanufacturing of a lithium battery having improved energy density andlifespan characteristics.

A binder composition for a second battery according to an embodiment ofthe present invention includes a first fluoropolymer binder including atetrafluoroethylene polymer binder, a second fluoropolymer binderincluding a vinylidene fluoride binder, and a non fluoropolymer binderincluding a repeating unit derived from an acryl monomer and a repeatingunit derived from an olefin monomer. The binder composition for asecondary battery includes the first fluoropolymer binder that providesexcellent flexibility of an electrode plate and swells less with respectto an electrolyic solution, the second fluoropolymer binder that retainsthe structure of an electrode during operation of a battery, and the nonfluoropolymer binder including a repeating unit derived from an acrylmonomer and a repeating unit derived from an olefin monomer thatimproves flexibility of an electrode plate, dispersibility of theconductive agent, and improved binding force of an electrode plate.Accordingly, a lithium battery including the binder composition for asecondary battery may have improved binding force, flexibility, anddispersibility of a conductive agent, and thus, improved cycliccharacteristics. A lithium battery including the binder composition mayhave improved cyclic characteristics at a high voltage of 4.3 or more.In some embodiments, the non fluoropolymer binder is a hydrogenatedacrylonitrile-butadiene binder, the first fluoropolymer binder is atetrafluorothylene polymer binder and the second fluoropolymer binder isa polyvinylidene fluoride.

In particular, since the binder composition for a second batteryincludes the first fluoropolymer binder including a tetrafluoroethylenepolymer binder and the non fluoropolymer binder including a repeatingunit derived from an acryl monomer and a repeating unit derived from anolefin monomer, an electrode formed using the binder composition mayinclude an electrode active layer having high mixture density and anincreased thickness, thereby leading to manufacturing of a lithiumbattery with high energy density and improved lifespan characteristics.

In some embodiments, the first fluoropolymer binder in the bindercomposition may be a copolymer of a tetrafluoroethylene monomer andother monomers. A homopolymer including only the tetrafluoroethylenemonomer may have poor flexibility. In some embodiments, the othermonomers used together with tetrafluoroethylene monomer are at least onefluorine-containing monomer selected from vinylidenefluoride,hexafluoropropylene, chlorotrifluoroethylene, andperfluoroalkylvinylether.

For example, the tetrafluoroethylene polymer binder that is the firstfluoropolymer binder may be a tetrafluoroethylene-vinylidenefluoridecopolymer, tetrafluoroethylene-hexafluoropropylene copolymer,tetrafluoroethylene-chlorotrifluoroethylene copolymer, ortetrafluoroethylene-perfluoroalkylvinylether.

In some embodiments, the first fluoropolymer binder may have, comparedto a typical vinylidene fluoride binder, improved stability andflexibility at high voltage. The typical vinylidene fluoride binder maynot include a polar functional group.

In some embodiments of the binder composition, the first fluoropolymerbinder may additionally include a polar functional group. Due to theinclusion of the additional polar functional group, binding force of anelectrode plate at a cathode may improve.

In some embodiments of the binder composition, the polar functionalgroup of the first fluoropolymer binder may be at least one selectedfrom the group consisting of a carboxylic acid group (—COOH), a sulfonicacid group (—SO₃H), a phosphoric acid group (—PO₄H₂), an acid anhydridegroup, and a hydroxy group (—OH), and a salt thereof, but is not limitedthereto, and the polar functional group may be any of various materialsthat are used as a polar functional group in the art.

For example, the introduction of the polar functional group into thefirst fluoropolymer binder may be performed by polymerizing a monomerincluding a carboxylic acid group, a monomer including a sulfonic acidgroup, a monomer including a phosphoric acid group, a monomer includingan acid anhydride group, a monomer including a hydroxy group, or amonomer including salts of the foregoing groups.

Examples of a monomer including a carboxylic acid group are amonocarboxylic acid and a derivative thereof, and a dicarboxylic acidand a derivative thereof. Examples of the monocarboxylic acid are anacrylic acid, a methacrylic acid, and a chrotonic acid. Examples of thederivative of the monocarboxylic acid are a 2-ethylacrylic acid,isochrotonic acid, a α-acethoxyacrylic acid, a β-trans-aryloxyacrylicacid, a α-chloro-β-E-methoxy acrylic acid, and a β-diaminoacrylic acid.Examples of the dicarboxylic acid are a maleic acid, a fumalic acid, andan itaconic acid. Examples of the derivative of a dicarboxylic acid aremethyl maleic acid, dimethyl maleic acid, phenyl maleic acid, chloromaleic acid, dichloro maleic acid, or fluoromaleic acid; and a maleicacid ester, such as diphenyl maleate, nonyl maleate, decyl maleate,dodecyl maleate, octadecyl maleate, or a fluoroalkyl maleate. Also, anacid anhydride that produces a carboxylic acid by hydrolysis may beused. Examples of an acid anhydride of the dicarboxylic acid are anmaleic anhydride, an acrylic anhydride, a methylmaleic anhydride, and adimethylmaleic anhydride. Also, a monoester and a diester ofα,β-ethylenically unsaturated polyvalent carboxylic acid, such as amonoethyl maleate, diethyl maleate, monobutyl maleate, dibutyl maleate,monoethyl fumareate, diethyl fumareate, monobutyl fumareate, dibutylfumareate, monocyclohexyl fumareate, dicyclohexyl fumareate, monoethylitaconate, diethyl itaconate, monobutyl itaconate, or dibutyl itaconate,may be further used.

Examples of a monomer having a sulfonic acid group are a vinylsulfonicacid, a methyl vinylsulfonic acid, a (meth)allylsulfonic acid, astyrenesulfonic acid, a (meth)acrylic acid-2-ethyl sulfonic acid, a2-acrylamid-2-methylpropanesulfonic acid, and a3-allyloxy-2-hydroxypropanesulfonic acid.

Examples of a monomer having a phosphoric acid group arephosphate2-(meth)acryloyloxyethyl, phosphoric acidmethyl-2-(meth)acryloyloxyethyl, and phosphoric acidethyl-(meth)acryloyloxyethyl.

Examples of a monomer having a hydroxyl group are an ethylenicallyunsaturated alcohol, such as (meth)allylalcohol, 3-butene-1-ol, or5-hexene-1-ol; alkanolesters of an ethylenically unsaturated carboxylicacid, such as acrylic acid-2-hydroxyethyl, acrylic acid-2-hydroxypropyl,methacrylic acid-2-hydroxyethyl, methacrylic acid-2-hydroxypropyl,maleic acid di-2-hydroxyethyl, maleic acid di-4-hydroxybutyl, oritaconic acid di2-hydroxypropyl; an ester of polyalkyleneglycol and(meth)acrylic acid represented by CH₂═CR¹—COO—(C_(n)H_(2n)O)_(m)—H (mindicates an integer of 2 to 9, n indicates an integer of 2 to 4, and R¹indicates a hydrogen or a methyl group); a mono(meth)ester acrylic acidof a dihydroxyester of a dicarboxylic acid, such as2-hydroxyethyl-2′-(meth)acryloyloxyphthalate, or2-hydroxyethyl-2′-(meth)acryloyloxysuccinate; vinylether, such as2-hydroxyethylvinylether or 2-hydroxypropylvinylether; a mono(meth)allylether of alkyleneglycol, such as (meth)allyl-2-hydroxyethylether,(meth)allyl-2-hydroxypropylether, (meth)allyl-3-hydroxypropylether,(meth)allyl-2-hydroxy butylether, (meth)allyl-3-hydroxybutylether,(meth)allyl-4-hydroxybutylether, or (meth)allyl-6-hydroxyhexylether;polyoxyalkyleneglycol(meth)monoallylether, such as diethyleneglycolmono(meth)allylether or dipropyleneglycolmono(meth)allylether;mono(meth)allylether of a halogen and hydroxy substituent of(poly)alkyleneglycol, such as glycerin mono(meth)allylether,(meth)allyl-2-chloro-3-hydroxypropylether, or(meth)allyl-2-hydroxy-3-chloropropylether; a mono(meth)allylether ofpolyphenol, such as eugenol or isoeugenol, or a halogen substituentthereof; and (meth)allylthioethers of alkyleneglycol, such as(meth)allyl-2-hydroxyethylthioether or(meth)allyl-2-hydroxypropylthioether.

From among these, in consideration of binding force among cathode activematerial particles, and binding force between a cathode active materiallayer and a current collector, a hydrophilic group may be a carboxylicacid group or a sulfonic acid group. In particular, in consideration ofhigh capturing efficiency of a transition metal ion eluted from thecathode active material, the hydrophilic group may be a carboxylic acidgroup.

In the binder composition for a secondary battery, an amount of therepeating unit including the polar functional group included in thefirst fluoropolymer binder may be 10 mole % or less. For example, anamount of the repeating unit including the polar functional groupincluded in the first fluoropolymer binder may be in a range of 0 to 9mol % or less. For example, an amount of the repeating unit includingthe polar functional group included in the first fluoropolymer bindermay be in a range of 0 to 8 mol % or less. For example, an amount of therepeating unit including the polar functional group included in thefirst fluoropolymer binder may be in a range of 0 to 7 mol % or less.For example, an amount of the repeating unit including the polarfunctional group included in the first fluoropolymer binder may be in arange of 0 to 5 mol % or less. When the amount of the repeating unitincluding the polar functional group is too high, flexibility of anelectrode plate may decrease.

In some embodiments, a weight average molecular weight of the firstfluoropolymer binder in the binder composition for a secondary batterymay be 100,000 g/mol or more. For example, a weight average molecularweight of the first fluoropolymer binder may be in a range of about100,000 to about 1,500,000 g/mol. For example, a weight averagemolecular weight of the first fluoropolymer binder may be in a range ofabout 300,000 to about 1,500,000 g/mol. For example, a weight averagemolecular weight of the first fluoropolymer binder may be in a range ofabout 500,000 to about 1,500,000 g/mol. The weight average molecularweight is a calculation result with respect to polystyrene standardobtained by gel permeation chromatography. Within these weight averagemolecular weight ranges of the first fluoropolymer binder, binding forceof an electrode plate may be further improved. When the weight averagemolecular weight is too small, stability of the slurry may decrease, andwhen the weight average molecular weight is too high, manufacturing ofthe electrode is difficult.

In some embodiments, an amount of the tetrafluoroethylene monomer unitin the first fluoropolymer binder may be 10 mol % or more. For example,an amount of the tetrafluoroethylene monomer unit in the firstfluoropolymer binder may be 30 mol % or more. For example, an amount ofthe tetrafluoroethylene monomer unit in the first fluoropolymer bindermay be 50 mol % or more. For example, an amount of thetetrafluoroethylene monomer unit in the first fluoropolymer binder maybe 70 mol % or more. For example, an amount of the tetrafluoroethylenemonomer unit in the first fluoropolymer binder may be 90 mol % or more.

In some embodiments, an amount of the first fluoropolymer binder in thebinder composition for a secondary battery may be, based on a totalweight of the binder composition, in a range of about 3 weight % toabout 27 weight %. For example, an amount of the first fluoropolymerbinder may be, based on a total weight of the binder composition, in arange of about 5 weight % to about 25 weight %. When the amount of thefirst fluoropolymer binder is less than 3 weight %, flexibility of anelectrode plate may decrease, and when the amount of the firstfluoropolymer binder is greater than 27 weight %, binding force of anelectrode plate may decrease and thus cracking of an electrode materiallayer (i.e., electrode mixture) may occur.

In some embodiments of the binder composition for a secondary battery,the second fluoropolymer binder including the vinylidine fluoride bindermay be a vinylidine binder that does not include a polar functionalgroup. The vinylidine binder that does not include a polar functionalgroup may be a typical vinylidine fluoride binder.

For example, the second fluoropolymer binder may be a homopolymer of avinylidene fluoride monomer, or a copolymer of a vinylidene fluoridemonomer and at least one fluorine-containing monomer selected fromhexafluoropropylene, chlorotrifluoroethylene, andperfluoroalkylvinylether. For example, the vinylidine monomer may be avinylidene fluoride homopolymer, a vinylidenefluoride-hexafluoropropylene copolymer, or a vinylidenefluoride-chlorotrifluoroethylene copolymer.

For example, in the binder composition for a secondary battery, thesecond fluoropolymer binder may include 50 mol % or more of thevinylidene fluoride monomer unit. For example, the second fluoropolymerbinder may include 60 mol % or more of the vinylidene fluoride monomerunit. For example, the second fluoropolymer binder may include 70 mol %or more of the vinylidene fluoride monomer unit. For example, the secondfluoropolymer binder may include 80 mol % or more of the vinylidenefluoride monomer unit. For example, the second fluoropolymer binder mayinclude 90 mol % or more of the vinylidene fluoride monomer unit.

In some embodiments, an amount of the second fluoropolymer binder in thebinder composition for a secondary battery may be, based on a totalweight of the binder composition, in a range of about 46 weight % toabout 94 weight %. For example, an amount of the second fluoropolymerbinder may be, based on a total weight of the binder composition, in arange of about 60 weight % to about 90 weight %. In some embodiments, anamount of the second fluoropolymer binder may be in a range of about 70weight % to about 85 weight % based on 100 parts by weight of a totalweight of the binder composition. When the amount of the secondfluoropolymer binder is less than 46 weight %, the active materialslurry of an electrode may have low stability, and when the amount ofthe second fluoropolymer binder is higher than 94 weight %, flexibilityand binding force of the electrode active material layer may decreaseand dispersibility of a conductive agent may decrease.

In some embodiments, a weight average molecular weight of the secondfluoropolymer binder in the binder composition for a secondary batterymay be 100,000 g/mol or more. For example, a weight average molecularweight of the second fluoropolymer binder may be in a range of about100,000 to about 1,500,000 g/mol. For example, a weight averagemolecular weight of the second fluoropolymer binder may be in a range ofabout 200,000 to about 1,200,000 g/mol. For example, a weight averagemolecular weight of the second fluoropolymer binder may be in a range ofabout 300,000 to about 1,000,000 g/mol. Within these weight averagemolecular weights of the second fluoropolymer binder, stability of theelectrode active material slurry may improve, and dispersibility of anactive material in the electrode active material slurry may furtherimprove.

In some embodiments, the non fluoropolymer binder in the bindercomposition for a second battery may include a repeating unit derivedfrom an acryl monomer and a repeating unit derived from an olefinmonomer.

In some embodiments, the acryl monomer in the non fluoropolymer bindermay be, for example, an acrylic acid alkylester, such as methylacrylate,ethylacrylate, n-propylacrylate, isopropylacrylate, n-butylacrylate,t-butylacrylate, pentylacrylate, hexylacrylate, heptylacrylate,octylacrylate, 2-ethylhexylacrylate, nonylacrylate, decylacrylate,laurylacrylate, n-tetra decylacrylate, or stearylacrylate; a methacrylicacid alkylester, such as methylmethacrylate, ethylmethacrylate,n-propylmethacrylate, isopropylmethacrylate, n-butylmethacrylic acid,t-butylmethacrylic acid, pentylmethacrylate, hexylmethacrylate,heptylmethacrylate, octylmethacrylate, 2-ethylhexylmethacrylate,nonylmethacrylate, decylmethacrylate, laurylmethacrylate,n-tetradecylmethacrylate, or stearylmethacrylate; di(meth)acrylic acidester, such as ethylenedi(meth)acrylate,diethyleneglycoldi(meth)acrylate, or ethyleneglycoldi(meth)acrylate; andmultifunctional ethylenically unsaturated monomer, such astrimethylolpropantri(meth)acrylate; but are not limited thereto. Forexample, the acryl monomer may be any of various materials that are usedas an acryl monomer in the art. These materials may be used alone or incombination thereof.

Examples of the olefin monomer in the non fluoropolymer binder may be anon-conjugated diene monomer, such as 1,4-pentadiene, 1,4-hexadiene,vinylnorbornene, or dicyclopentadiene; an α-olefin monomer, such asethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, or1-octene, but are not limited thereto, and the olefin monomer may be anyof various materials that are used as an olefin monomer in the art.These materials may be used alone or in combination thereof.

For example, the non fluoropolymer binder may be apoly(ethylene-acrylate) binder, a poly(propylene-acrylate) binder, or apoly(butylene-acrylate) binder.

In some embodiments, the poly(ethylene-acrylate) binder may be, forexample, poly(ethylene-methyl(meth)acrylate),poly(ethylene-ethyl(meth)acrylate), poly(ethylene-propyl(meth)acrylate),poly(ethylene-butyl(meth)acrylate),poly(ethylene-2-ethylhexyl(meth)acrylate), or a copolymer of thesematerials and at least one of acrylonitrile and (meth)acrylic acid.

In some embodiments, the poly(propylene-acrylate) binder may be, forexample, poly(propylene-methyl(meth)acrylate),poly(propylene-ethyl(meth)acrylate),poly(propylene-propyl(meth)acrylate),poly(propylene-butyl(meth)acrylate),poly(propylene-2-ethylhexyl(meth)acrylate), or a copolymer of thesematerials and at least one of acrylonitrile and (meth)acrylic acid.

In some embodiments, the poly(butylene-acrylate) binder may be, forexample, poly(butylene-methyl(meth)acrylate),poly(butylene-ethyl(meth)acrylate), poly(butylene-propyl(meth)acrylate),poly(butylene-butyl(meth)acrylate),poly(butylene-2-ethylhexyl(meth)acrylate), or a copolymer of thesematerials and at least one of acrylonitrile and (meth)acrylic acid.

For example, the non fluoropolymer binder may bepoly(ethylene-acrylonitrile), poly(ethylene-acrylonitrile-(meth)acrylicacid), poly(prothylene-acrylonitrile),poly(prothylene-acrylonitrile-(meth)acrylic acid),poly(butylene-acrylonitrile), orpoly(butylene-acrylonitrile-(meth)acrylic acid).

In some embodiments, an amount of a repeating unit derived from the anacryl monomer in the non fluoropolymer binder may be in a range of about1 weight % to about 70 weight %, for example, about 2 weight % to about50 weight %, for example, about 5 weight % to about 30 weight %, forexample, about 10 weight % to about 25 weight %. When the amount of therepeating unit derived from the acryl monomer in the non fluoropolymerbinder is too high, solubility of the binder with respect to anelectrolytic solution increases, and thus cyclic characteristics of abattery may decrease. Also, when the amount of the repeating unitderived from the acryl monomer in the non fluoropolymer binder is toolow, dispersibility of an electrode active material may decrease andthus, appropriate cathode active material slurry may not be obtained,leading to a decrease in homogeneity of an obtained electrode.

For example, the repeating unit derived from the acryl monomer in thenon fluoropolymer binder may include a nitrile group. Since the nonfluoropolymer binder includes a repeating unit including a nitrilegroup, dispersibility of an electrode active material in an electrodeactive material slurry for forming an electrode active material layermay improve, and thus, the slurry may be preserved in a stable state fora long period of time. Also, flexibility of the electrode activematerial layer may improve.

For example, the repeating unit derived from the olefin monomer in thenon fluoropolymer binder may include a conjugated diene monomer. In thenon fluoropolymer binder, a repeating unit derived from a conjugateddiene monomer may be a repeating unit having a linear alkylenestructure. In a polymer that constitutes the non fluoropolymer binder, arepeating unit having a linear alkylene structure may have 4 or morecarbon atoms, and the number of carbon atoms may be, for example, in arange of 4 to 16, and for example, in a range of 4 to 12. For example,the conjugated diene monomer may be a 1,3-butadiene.

When a repeating unit having a non-polar linear alkylene structure isintroduced into a polymer that constitutes the non fluoropolymer binder,dispersibility of a conductive agent, which is added to the electrodeactive material slurry, improves and thus, uniform electrode may beeasily manufactured. Also, since a conductive agent is homogeneouslydispersed in an electrode, internal resistance of a cathode maydecrease, and as a result, cyclic characteristics and outputcharacteristics of a lithium battery including the cathode may improve.Also, since the linear alkylene repeating unit is introduced, swellingof an electrode with respect to an electrolytic solution may beappropriately adjusted and thus, characteristics of a battery mayimprove.

In some embodiments, an amount of the repeating unit having the linearalkylene structure having four or more carbon atoms in the nonfluoropolymer binder may be in a range of about 30 to about 99 weight %,for example about 50 to about 98 weight %, for example about 70 to about95 weight %, or for example, about 75 weight % to about 90 weight %.

The non fluoropolymer binder may additionally include a repeating unitincluding a polar functional group. The polar functional group may be afunctional group that generates protons in an aqueous solvent, or a saltprepared by substituting a proton with a cation, and a detailed examplethereof is a carboxylic acid group, a sulfonic acid group, a phosphoricacid group, a hydroxyl group, or a salt thereof. Due to the introductionof the polar functional group into a polymer that constitutes the nonfluoropolymer binder, binding force may improve.

In some embodiments, an amount of the repeating unit including the polarfunctional group in the non fluoropolymer binder may be in a range ofabout 0.05 to about 10 weight %, for example, about 0.1 to about 8weight %, or for example, about 1 to about 6 weight %.

In some embodiments, an iodine value of the non fluoropolymer binder maybe 100 or less. The iodine value of the non fluoropolymer binder may be,for example, higher than about 0 to about 90 mg/100 mg, for example,higher than about 0 to about 30 mg/100 mg, for example, higher thanabout 0 to about 10 mg/100 mg. When the iodine value of the nonfluoropolymer binder is higher than 100 mg, unsaturated bond included inthe binder may lead to a decrease in stability at oxidation potential,thereby leading to a decrease in cyclic characteristics. In someembodiments, a weight average molecular amount of the non fluoropolymerbinder may be in a range of about 100,000 to about 1,000,000 g/mol. Forexample, a weight average molecular amount of the non fluoropolymerbinder may be in a range of about 100,000 to about 800,000 g/mol, forexample, about 100,000 to about 600,000 g/mol, for example, about100,000 to about 500,000 g/mol, or for example, about 100,000 to about300,000 g/mol. Within these weight average molecular weight ranges ofthe non fluoropolymer binder, flexibility of an electrode anddispersibility of a conductive agent may improve.

For example, the non fluoropolymer binder includes a repeating unithaving a nitrile group and a repeating unit having a linear alkylenestructure having two or more carbon atoms, and may optionally furtherinclude a repeating unit having a polar functional group. In someembodiments, the non fluoropolymer binder may be prepared bypolymerizing a monomer deriving a repeating unit having a nitrile group,a monomer deriving a repeating unit including a linear alkylenestructure, and optionally, a monomer deriving a repeating unit having apolar functional group. Also, the linear alkylene structure unit may beprepared in such a way that a polymer having a repeating unit having anunsaturated bond is obtained and then, hydrogen is added thereto. Bycontrolling the amount of the hydrogen added, the iodine value of thenon fluoropolymer binder may be controlled.

In some embodiments, the monomer deriving a repeating unit having anitrile group in the non fluoropolymer binder may be an α,β-ethyleneunsaturated nitrile monomer. In some embodiments, the α,β-ethyleneunsaturated nitrile monomer may not be particularly limited and may beany one of various α,β-ethylene unsaturated compounds having a nitrilegroup, and examples of the α,β-ethylene unsaturated nitrile monomer areα-halogenoacrylonitrile, such as acrylonitrile; α-chloroacrylonitrile,or α-bromoacrylonitrile; and α-alkylacrylonitrile, such asmetacrylonitrile. For example, the α,β-ethylenically unsaturated nitrilemonomer may be acrylonitrile or metacrylonitrile. These materials may beused alone or in combination thereof.

How the repeating unit having the linear alkylene structure isintroduced into the non fluoropolymer binder is not particularlylimited. For example, a conjugated diene monomer unit is introduced, andthen, a hydrogen is added thereto. In some embodiments, the conjugateddiene monomer may be a conjugated diene having four or more carbonatoms, such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, or1,3-pentadiene. For example, the conjugated diene monomer may be1,3-butadiene may be used, and these materials may be used alone or incombination thereof.

In some embodiments, the non fluoropolymer binder may be used in theform of a dispersion solution in which the binder is dispersed in adispersion medium (water or organic solvent) or in which the binder isdissolved in the dispersion medium (hereinafter, the dispersion solutionwill be referred to as a binder dispersion solution). The dispersionmedium is not particularly limited as long as the medium allows thebinder to homogeneously disperse or dissolve. The dispersant may bewater that is environmentally friendly and dries quickly. Examples ofthe organic solvent are cyclic aliphatic hydrocarbons, such ascyclopentane or cyclohexane; aromatic hydrocarbons, such as toluene,xylene, or ethylbenzene; ketones, such as acetone, ethylmethylketone,diisopropylketone, cyclohexanone, methylcyclohexanone, orethylcyclohexanone; chlorinated aliphatic hydrocarbons, such asmethylenechloride, chloroform, or carbon tetrachloride; esters, such asethylacetate, butylacetate, γ-butylolactone, or ε-caprolactone;acetonitriles, such as acetonitrile or propionitrile; ethers, such astetrahydrofuran or ethyleneglycoldiethylether; alcohols, such asmethanol, ethanol, isopropanol, ethyleneglycol, ethyleneglycolmonomethyl ether; and amides, such as N-methyl pyrrolidone orN,N-dimethylformimide. These dispersants may be used alone or incombination thereof. For example, water or N-methylpyrrolidone (NMP) maybe chosen for use as the dispersant because water and NMP suppressevaporation of an electrode active material slurry to improve flatnessof an electrode.

When the non fluoropolymer binder is dispersed in the form of particlesin the dispersion medium, an average particle diameter (dispersionparticle diameter) of the binder dispersed in the particle state may bein a range of about 10 to about 500 nm, for example about 20 to about300 nm, or for example about 50 to about 200 nm. Within these averageparticle diameter ranges of the binder, an electrode formed using thebinder may have improved stiffness and flexibility.

When the non fluoropolymer binder is dispersed in the form of particlesin a dispersion medium, a solid content of the binder dispersionsolution may be in a range of, for example, about 15 to about 70 weight%, for example, about 20 to about 65 weight %, or for example, about 30to about 60 weight %. Within these solid content ranges, the electrodeactive material slurry may be easily prepared.

Glass transition temperature (Tg) of the non fluoropolymer binder may bein a range of about −40° C. to about 30° C. For example, a Tg of the nonfluoropolymer binder may be in a range of about −40° C. to about 25° C.For example, a Tg of the non fluoropolymer binder may be in a range ofabout −40° C. to about 20° C. For example, a Tg of the non fluoropolymerbinder may be in a range of about −40° C. to about 15° C. For example, aTg of the non fluoropolymer binder may be in a range of about −40° C. toabout 5° C. Within these Tg ranges of the non fluoropolymer binder, anelectrode including the non fluoropolymer binder may have improvedstiffness and flexibility. The Tg of the non fluoropolymer binder may beappropriately controlled by combining various monomers. When the Tg ofthe non fluoropolymer binder is lower than −40° C., an electrode platemay have a sticky surface, causing difficulties in manufacturing abattery, and when the Tg of the non fluoropolymer binder is higher than30° C., flexibility of an electrode may decrease.

In some embodiments, an amount of the non fluoropolymer binder in thebinder composition for a second battery may be in a range of about 3weight % to about 27 weight % based on 100 weight % of a total weight ofthe binder composition. An amount of the non fluoropolymer binder in thebinder composition for a second battery may be in a range of about 5weight % to about 25 weight % based on 100 parts by weight of a totalweight of the binder composition. In some embodiments, an amount of thenon fluoropolymer binder in the binder composition for a second batterymay be in a range of about 10 weight % to about 20 weight % based on 100parts by weight of a total weight of the binder composition. When theamount of the non fluoropolymer binder is less than 3 weight %,flexibility of an electrode plate and dispersibility of a conductiveagent may decrease, and when the amount of the non fluoropolymer binderis higher than 27 weight %, lifespan of lithium battery may decreasebecause of high swelling of the non fluoropolymer binder with respect toelectrolytic solution.

A cathode according to an embodiment of the present invention includes acathode active material, a conductive agent, and the binder compositionfor a second battery.

In some embodiments, an amount of the binder composition in the cathodemay be in a range of about 0.5 to about 5 parts by weight based on 100parts by weight of the cathode active material. For example, an amountof the binder composition in the cathode may be in a range of about 0.5to about 4 parts by weight based on 100 parts by weight of the cathodeactive material. For example, an amount of the binder composition in thecathode may be in a range of about 0.5 to about 3 parts by weight basedon 100 parts by weight of the cathode active material. For example, anamount of the binder composition in the cathode may be in a range ofabout 0.5 to about 2 parts by weight based on 100 parts by weight of thecathode active material. For example, an amount of the bindercomposition in the cathode may be in a range of about 0.5 to about 1.5parts by weight based on 100 parts by weight of the cathode activematerial. When the amount of the binder composition in the cathode ishigher than 5 parts by weight, amounts of an electrode active materialand a conductive agent may relatively decrease and thus, dischargecapacitance decreases and energy density decreases, and when the amountof the binder composition is less than 0.5 parts by weight, bindingforce and flexibility of the electrode active material layer maydecrease.

In some embodiments, a weight of a cathode mixture in the cathode perunit area may be higher than 40 mg/cm². For example, a weight of acathode mixture in the cathode per unit area may be higher than 45mg/cm². For example, a weight of a cathode mixture in the cathode perunit area may be higher than 50 mg/cm². When the weight of a cathodemixture in the cathode per unit area is higher than 40 mg/cm², thethickness of an active material layer increases, thus, energy density ofan electrode may improve. The cathode mixture used herein refers to acathode active material layer including a cathode active material, aconductive agent, and a binder, prepared by drying the cathode activematerial slurry.

In some embodiments, a mixture density of the cathode may be 3.5 g/cc ormore. For example, a mixture density of the cathode may be 3.7 g/cc ormore. For example, a mixture density of the cathode may be 3.9 g/cc ormore. For example, a mixture density of the cathode may be 4.0 g/cc ormore. For example, a mixture density of the cathode may be 4.1 g/cc ormore. For example, a mixture density of the cathode may be 4.2 g/cc ormore. When the cathode has 3.5 g/cc or more of the mixture density,energy density of the cathode may improve.

In some embodiments, the cathode may be manufactured by, for example,molding a cathode active material composition including the cathodeactive material, the conductive agent, and the binder composition for asecond battery into a predetermined shape, or coating the cathode activematerial composition on a current collector, such as a copper foil.

In detail, a cathode active material composition including a cathodeactive material, a conductive agent, the binder composition describedabove, and a solvent is prepared. In some embodiments, the cathodeactive material composition may be directly coated on a metal currentcollector to prepare a cathode plate. In another embodiment, the cathodeactive material composition is cast on a separate support, and then, afilm exfoliated from the support is laminated on a metal currentcollector to prepare a cathode plate. The method of forming the cathodeis not limited thereto and any other method may also be used to form thecathode.

As the cathode active material, at least one selected from a lithiumcobalt oxide, a lithium nickel cobalt, manganese oxide, a lithium nickelcobalt aluminum oxide, a lithium iron phosphate oxide, and lithiummanganese oxide may be used. However, the cathode active material is notlimited thereto. For example, any one of various materials that are usedas a cathode active material in the art may be used.

For example, the cathode active material may be a compound representedby any one of Li_(a)A_(1-b)B¹ _(b)D¹ ₂ (wherein 0.90≦a≦1.8, and0≦b≦0.5); Li_(a)E_(1-b)B¹ _(b)O_(2-c)D¹ _(c) (wherein 0.90≦a≦1.8,0≦b≦0.5, and 0≦c≦0.05); LiE_(2-b)B¹ _(b)O_(4-c)D¹ _(c) (wherein 0≦b≦0.5,and 0≦c≦0.05); Li_(a)Ni_(1-b-c)Co_(b)B¹ _(c)D¹ _(α) (wherein 0.90≦a≦1.8,0≦b≦0.5, 0≦c≦0.05, and 0≦α≦2); Li_(a)Ni_(1-b-c)Co_(b)B¹ _(c)O_(2-α)F¹_(α) (wherein 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0≦α≦2);Li_(a)Ni_(1-b-c)Co_(b)B¹ _(c)O_(2-α)F¹ ₂ (wherein 0.90≦a≦1.8, 0≦b≦0.5,0≦c≦0.05, and 0≦α≦2); Li_(a)Ni_(1-b-c)Mn_(b)B¹ _(c)D¹ _(α) (wherein0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0≦α≦2); Li_(a)Ni_(1-b-c)Mn_(b)B¹_(c)O_(2-α)F¹ _(α) (wherein 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0≦α≦2);Li_(a)Ni_(1-b-c)Mn_(b)B¹ _(c)O_(2-α)F¹ ₂ (wherein 0.90≦a≦1.8, 0≦b≦0.5,0≦c≦0.05, and 0≦α≦2); Li_(a)Ni_(b)E_(c)G_(d)O₂ (wherein 0.90≦a≦1.8,0≦b≦0.9, 0≦c≦0.5, and 0.001≦d≦0.1.); Li_(a)Ni_(b)Co_(c)Mn_(d)GeO₂(wherein 0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0≦d≦0.5, and 0.001≦e≦0.1.);Li_(a)NiG_(b)O₂ (wherein 0.90≦a≦1.8, and 0.001≦b≦0.1.); Li_(a)CoG_(b)O₂(wherein 0.90≦a≦1.8, and 0.001≦b≦0.1.); Li_(a)MnG_(b)O₂ (wherein0.90≦a≦1.8, and 0.001≦b≦0.1.); Li_(a)Mn₂G_(b)O₄ (wherein 0.90≦a≦1.8, and0.001≦b≦0.1.); LiQS₂; V₂O₅; LiV₂O₅; LiI¹O₂; LiNiVO₄; Li_((3-f))J₂(PO₄)₃(0≦f≦2); Li_((3-f))Fe₂(PO₄)₃ (0≦f≦2); and LiFePO₄.

In the formulae above, A is Ni, Co, Mn, or a combination thereof; B¹ isAl, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare-earth element, or acombination thereof; D¹ is O (oxygen), F (fluorine), S (sulfur), P(phosphorus), or a combination thereof; E is Co, Mn, or a combinationthereof; F¹ is F (fluorine), S (sulfur), P (phosphorus), or acombination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or acombination thereof; Q is Ti, Mo, Mn, or a combination thereof; I¹ isCr, V, Fe, Sc, Y, or a combination thereof; and J is V, Cr, Mn, Co, Ni,Cu, or a combination thereof.

These compounds may have a coating layer on their surfaces, or thesecompounds may be mixed with a compound having a coating layer. Thecoating layer may include an oxide of a coating element, a hydroxide ofa coating element, an oxyhydroxide of a coating element, an oxycarbonateof a coating element, or a hydroxycarbonate of a coating element. Thesecompounds that form the coating layer may be amorphous or crystalline.As a coating element included in the coating layer, Mg, Al, Co, K, Na,Ca, Si, Ti, V, Sn, Ge, Ga, B (boron), As, Zr, or a mixture thereof maybe used. In some embodiments, the coating layer may be formed by usingany one of various coating methods that are performed using thecompounds and the elements and do not affect properties of the cathodeactive material (for example, spray coating, immersion, or the like).These coating methods are known to one of ordinary skill in the art andthus, are not described in detail herein.

For example, LiNiO₂, LiCoO₂, LiMn_(x)O_(2x) (x=1, 2), LiNi_(1-x)Mn_(x)O₂(0<x<1), LiNi_(1-x-y)Co_(x)Mn_(y)O₂ (0≦x≦0.5, 0≦y≦0.5), LiFeO₂, V₂O₅,TiS, or MoS may be used.

In some embodiments, the cathode active material may be at least oneselected from compounds represented by Formulae 1 to 7 below:

pLi₂MO_(3-(1-p))LiMeO₂  Formula 1

wherein 0<p≦0.8, M is at least one metal selected from the groupconsisting of Ru, Rh, Pd, Os, Ir, Pt, Mg, Ca, Sr, Ba, Ti, Zr, Nb, Mo, W,Zn, Al, Si, Ni, Mn, Cr, Fe, Mg, Sr, V, and a rare earth element, and Meis at least one metal selected from the group consisting of Ti, V, Cr,Mn, Fe, Co, Ni, Cu, Al, Mg, Zr, and B (boron),

Li[Li_(x)Me_(y)]O_(2+d)  Formula 2

wherein x+y=1, 0<x<1, 0≦d≦0.1, and Me is at least one metal selectedfrom Mn, V, Cr, Fe, Co, Ni, Zr, Re, Al, B, Ge, Ru, Sn, Ti, Nb, Mo, andPt,

xLi₂MO_(3-y)LiMeO_(2-z)Li_(1+d)M′_(2−d)O₄  Formula 3

wherein x+y+z=1; 0<x<1, 0<y<1, 0<z<1; 0≦d≦0.33, M is at least one metalselected from the group consisting of Mg, Ca, Sr, Ba, Ti, Zr, Nb, Mo, W,Zn, Al, Si, Ni, Mn, Cr, Fe, Mg, Sr, V, and rare earth element, Me is atleast one metal selected from the group consisting of Ti, V, Cr, Mn, Fe,Co, Ni, Cu, Al, Mg, Zr, and B (boron), and M′ is at least one metalselected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Al,Mg, Zr, and B (boron),

Li_(x)Co_(1-y)M_(y)O_(2-α)X_(α)  Formula 4

Li_(x)Co_(1-y-z)Ni_(y)M_(z)O₂₋₊X_(α)  Formula 5

Li_(x)Mn_(2-y)M_(y)O_(4-α)X_(α)  Formula 6

Li_(x)Co_(2-y)M_(y)O₄₋₊X_(α)  Formula 7

Li_(x)Me_(y)M_(z)PO_(4-α)X_(α)  Formula 8

wherein in the formulae above, 0.90≦x≦1.1, 0≦y≦0.9, 0≦z≦0.5, 1−y−z>0,0≦α≦2, Me is at least one metal selected from the group consisting ofTi, V, Cr, Mn, Fe, Co, Ni, Cu, Al, Mg, Zr, and B (boron), M is at leastone metal selected from the group consisting of Mg, Ca, Sr, Ba, Ti, Zr,Nb, Mo, W, Zn, Al, Si, Ni, Mn, Cr, Fe, Mg, Sr, V, and a rare earthelement, and X is at least one metal selected from the group consistingof O (oxygen), F (fluorine), S (sulfur), and P (phosphorus).

Examples of the conductive agent are acetylene black, ketjen black,natural graphite, artificial graphite, carbon black, carbon fiber, andmetal powder and metal fiber of copper, nickel, aluminum, or silver, andat least one of conductive materials, such as polyphenylene derivatives.However, the conductive agent is not limited thereto, and may be any oneof various materials that are used as a conductive agent in the art.Also, the crystalline carbonaceous material may be additionally used foruse as the conductive agent.

A typical binder may be additionally used in addition to the bindercomposition for a second battery. Examples of the typical binder are avinylidene fluoride/hexafluoropropylene copolymer,polyvinylidenefluoride (PVDF), polyacrylonitrile, polymethylmetacrylate,polytetrafluoroethylene, a mixture thereof, and a styrene butadienerubber-based polymer, but are not limited thereto, and any one ofmaterials that are used as a binder in the art may be used herein.

As the solvent, N-methylpyrrolidone, acetone, or water may be used.However, the solvent is not limited thereto, and any one of variousmaterials that are used in the art may be used herein.

Amounts of the cathode active material, the conductive agent, thetypical binder, and the solvent may be the same as used in a typicallithium battery. According to the purpose and structure of a lithiumbattery, one or more of the conductive agent, the binder, and thesolvent may not be used.

A lithium battery according to an embodiment of the present disclosureincludes the cathode. An example of a method of manufacturing a lithiumbattery is described below.

First, a cathode is prepared by using the method described above.

Then, an anode active material composition including a anode activematerial, a conductive agent, a binder, and a solvent is prepared. Theanode active material composition is directly coated and dried on themetal current collector to prepare an anode plate. According to anotherembodiment of the present disclosure, the anode active materialcomposition is cast on a separator support and a film exfoliated fromthe support is laminated on a metal current collector to prepare ananode electrode plate.

In some embodiments, the anode active material may be a non-carbonaceousmaterial. In some embodiments, the anode active material may include atleast one selected from a metal that is alloyable with lithium, an alloyof a metal that is alloyable with lithium, and an oxide of a metal thatis alloyable with lithium.

For example, the lithium-alloyable metal may be Si, Sn, Al, Ge, Pb, Bi,Sb, Si—Y alloy (where Y is alkali metal, alkali earth metal, a Group 13element, a Group 16 element, transition metal, rare earth element, or acombination thereof element and is not Si), or Sn—Y alloy (where Y isalkali metal, alkali earth metal, a Group 13 element, a Group 16element, transition metal, rare earth element, or a combination thereofelement and is not Sn). In some embodiments, the element Y may be Mg,Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc,Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al,Ga, Sn, In, Ge, P, As, Sb, Bi, S, Se, Te, Po, or a combination thereof.

For example, the transition metal oxide may be titanium oxide, avanadium oxide, or a lithium vanadium oxide.

For example, the transition metal oxide may be SnO₂, SiO_(x)(0<x<2), orthe like.

For example, the anode active material may be at least one selected fromSi, Sn, Pb, Ge, Al, SiO_(x) (0<x≦2), SnO_(y) (0<y≦2), Li₄Ti₅O₁₂, TiO₂,LiTiO₃, and Li₂Ti₃O₇, but is not limited thereto, and any one of variousnon-carbonaceous anode active materials that are used in the art may beused herein.

Also, a composite of the non-carbonaceous anode active material and acarbonaceous material may be used. Also, in addition to thenon-carbonaceous material, a carbonaceous material may be additionallyincluded.

In some embodiments, the carbonaceous material may be a crystallinecarbon, an amorphous carbon, or a mixture thereof. In some embodiments,the crystalline carbon may be natural or artificial graphite that isnon-shaped, tabular, flake, spherical, or fibrous, and the amorphouscarbon may be soft carbon (cold calcined carbon) or hard carbon,meso-phase pitch carbide, calcinded corks, or the like.

In some embodiments, the conductive agent, the binder, and the solventincluded in the anode active material composition may be the same asthose used in the cathode active material composition. Also, aplasticizer may be further included in at least one of the cathodeactive material composition and the anode active material composition toform pores in an electrode plate.

Amounts of the anode active material, the conductive agent, the typicalbinder, and the solvent may be the same as used in a typical lithiumbattery. According to the purpose and structure of a lithium battery,one or more of the conductive agent, the binder, and the solvent may notbe used.

Then, a separator which is to be inserted between the cathode and theanode is prepared. The separator may be any one of various materialsthat are typically used in a lithium battery. A material for forming theseparator may be a material that has low resistance to ion migration ofan electrolyte and has excellent electrolytic solution retainingcapability. For example, the separator forming material may be selectedfrom glass fiber, polyester, polyethylene, polypropylene,polytetrafluoroethylene (PTFE), and a combination thereof, each of whichmay be in a non-woven fabric or woven fabric form. For example, for usein a lithium ion battery, a rollable separator formed of polypropylenemay be used, and for use in a lithium ion polymer battery, a separatorthat has excellent organic electrolytic solution-retaining capabilitymay be used. For example, these separators may be prepared by using thefollowing method.

In some embodiments, a separator composition is prepared by mixing apolymer resin, a filler, and a solvent. In some embodiments, theseparator composition may be directly coated or dried on an electrode tocomplete the formation of the separator. In some embodiments, theseparator composition may be cast on a separate support and then a filmseparated from the support is laminated on an electrode, therebycompleting the formation of the separator.

A polymer resin used in preparing the separator may not be particularlylimited, and all the materials used for a binder of an electrode platemay be used. For example, a vinylidene fluoride/hexafluoropropylenecopolymer, polyvinylidenefluoride (PVDF), polyacrylonitrile,polymethylmetacrylate, or a mixture thereof may be used.

Then, an electrolyte may be prepared.

For example, the electrolyte may be an organic electrolytic solution.According to an embodiment of the present disclosure, the electrolytemay be solid. For example, boron oxide, lithiumoxynitrite, or the likemay be used, but the electrolyte may not be limited thereto, and theelectrolyte may be any one of various materials that are used as a solidelectrolyte in the art. The solid electrolyte may be formed on an anodeby, for example, sputtering.

For example, an organic electrolytic solution may be prepared. Theorganic electrolytic solution may be prepared by dissolving a lithiumsalt in an organic solvent.

The organic solvent may be any one of various materials that are used asan organic solvent in the art. For example, the organic solvent may beselected from propylenecarbonate, ethylenecarbonate,fluoroethylenecarbonate, butylenecarbonate, dimethylcarbonate,diethylcarbonate, methylethylcarbonate, methylpropylcarbonate,ethylpropylcarbonate, methylisopropylcarbonate, dipropylcarbonate,dibutylcarbonate, benzonitrile, acetonitrile, tetrahydrofurane,2-methyltetrahydrofurane, α-butyrolactone, dioxorane, 4-methyldioxorane,N,N-dimethylformamide, dimethylacetamide, dimethylsufloxide, dioxane,1,2-dimethoxyethane, sulforane, dichloroethane, chlorobenzene,nitrobenzene, diethyleneglycol, dimethylether, and a combinationthereof.

In some embodiments, the lithium salt may be any one of various lithiumsalts used in the art. For example, LiPF₆, LiBF₄, LiSbF₆, LiAsF₆,LiClO₄, LiCF₃SO₃, Li(CF₃SO₂)₂N, LiC₄F₉SO₃, LiAlO₂, LiAlCl₄,LiN(C_(x)F_(2x+1)SO₂)(C_(y)F_(2y+1)SO₂) (wherein x and y are naturalnumbers of 1 to 20, respectively), LiCl, LiI or a mixture thereof may beused.

Referring to FIG. 1, a lithium battery 1 includes a cathode 3, an anode2, and a separator 4. In some embodiments, the cathode 3, the anode 2,and the separator 4 are wound or folded to be placed in a battery case5. Subsequently, an organic electrolytic solution is injected into thebattery case 5, and the result structure is sealed with a cap assembly6, thereby completing the manufacturing of the lithium battery 1. Insome embodiments, the battery case 5 may be cylindrical, rectangular,and thin-film shape. For example, the lithium battery may be thin-filmbattery. In some embodiments, the lithium battery may be a lithium ionbattery. In some embodiments, the lithium battery may be a lithiumpolymer battery.

In some embodiments, a separator may be interposed between the cathodeand the anode to form a battery assembly. In some embodiments, aplurality of battery assemblies may be stacked or rolled in a bi-cellstructure and then impregnated with an organic electrolytic solution,and the obtained result is housed in a pouch, followed by sealing,thereby completing the manufacture of a lithium ion polymer battery.

Also, a plurality of the battery assemblies may be stacked to form abattery pack, and the battery pack may be used in various devices thatrequire high capacitance and high power output. For example, the batteryassemblies may be used in a notebook computer, a smartphone, an electricvehicle, or the like.

In particular, a lithium battery may be suitable for use in an electricvehicle (EV) due to its high energy density and lifespancharacteristics. For example, the lithium battery is suitable for use ina hybrid car, such as a plug-in hybrid electric vehicle (PHEV).

The embodiments of the present disclosure are described in detail withreference to Examples below. However, Examples are presented herein forillustrative purpose only, and do not limit the scope of the presentdisclosure.

Preparation of a Binder Preparation of Cathode and Lithium BatteryExample 1

A cathode active material slurry including a mixture (Umicore) includingLCO (LiCoO₂) and NCM (LiNi_(0.3)Co_(0.5)Mn_(0.2)O₂) at a weight ratio of8:2, carbon black (Ketchen black ECP, SP5090, Lion Corp., Tokyo, Japan),and a binder at a weight ratio of 97.8:1.2:1 was prepared.

A binder composition was prepared in such a way that the binder of thecathode active material slurry included a first fluoropolymer binder, asecond fluoropolymer binder, and a non fluoropolymer binder at a weightratio of 10:80:10.

In detail, carbon black was added to a non-fluoropolymer binder solution(a binder solution in which a hydrogenated acrylonitrile-butadienebinder was dispersed in NMP, BM-720H, a weight average molecularamount=300,000 g/mol, Tg=−30° C., Nippon Zeon Co. Ltd., Tokyo, Japan),and the mixture was stirred by using a Planetary centrifugal mixer(hereinafter referred to as Thinky mixer, Thinky Corporation, LagunaHills, Calif., USA) at a rotation rate of 2000 rpm for 5 minutes toprepare a conductive agent slurry.

Then, a second fluoropolymer binder solution (SOLEF 6020, PVDF, weightaverage molecular amount=700,000 g/mol, Solvay, Belgium) and the cathodeactive material were added to the conductive agent slurry, and then, themixture was stirred by using a Thinky mixer at a rotation rate of 2000rpm for 5 minutes to prepare a first active material slurry.

Subsequently, a first fluoropolymer binder solution (VT471, P(TFE-VDF),weight average molecular weight=350,000 g/mol, Daikin, Osaka, Japan) wasadded to the first active material slurry, and then, the mixture wasstirred by using a Thinky mixer at a rotation rate of 500 rpm for 5minutes to prepare a second active material slurry.

The second active material slurry was coated on an aluminum foil havinga thickness of 12 μm to form a coating film having a thickness of 102μm, and then dried at a temperature of 110° C. for 2 hours, and pressedto make the thickness thereof to be 71 μm, thereby completing themanufacture of a cathode electrode plate. Then, a coin cell (CR2016type) having a diameter of 32 mm was prepared.

To manufacture the cell, metal lithium was used as a counter electrode,a polyethylene separator (Star® 20, Asahi Kasei, Tokyo Japan) having athickness of 20 μm was used as a separator, and 1.15M LiPF₆ dissolved ina mixed solvent of ethylenecarbonate (EC):ethylmethylcarbonate(EMC):diethylcarbonate (DEC) (a volumetric ratio of 3:3:4) was used asan electrolyte

Example 2

A cathode active material slurry, a cathode, and a lithium battery wereprepared in the same manner as in Example 1, except that a weight ratioof the first fluoropolymer binder, the second fluoropolymer binder, andthe non fluoropolymer binder in the binder composition was 5:80:15.

Example 3

A cathode active material slurry, a cathode, and a lithium battery wereprepared in the same manner as in Example 1, except that a weight ratioof the first fluoropolymer binder, the second fluoropolymer binder, andthe non fluoropolymer binder in the binder composition was 15:70:15.

Example 4

A cathode active material slurry, a cathode, and a lithium battery wereprepared in the same manner as in Example 1, except that a weight ratioof the first fluoropolymer binder, the second fluoropolymer binder, andthe non fluoropolymer binder in the binder composition was 25:60:15.

Example 5

A cathode active material slurry, a cathode, and a lithium battery wereprepared in the same manner as in Example 1, except that a weight ratioof the first fluoropolymer binder, the second fluoropolymer binder, andthe non fluoropolymer binder in the binder composition was 15:60:25.

Example 6

A cathode active material slurry, a cathode, and a lithium battery wereprepared in the same manner as in Example 1, except that a weight ratioof the first fluoropolymer binder, the second fluoropolymer binder, andthe non fluoropolymer binder in the binder composition was 25:50:25.

Comparative Example 1

A cathode active material slurry, a cathode, and a lithium battery wereprepared in the same manner as in Example 1, except that a weight ratioof the first fluoropolymer binder, the second fluoropolymer binder, andthe non fluoropolymer binder in the binder composition was 30:40:30.

Comparative Example 2

A cathode active material slurry, a cathode, and a lithium battery wereprepared in the same manner as in Example 1, except that a weight ratioof the first fluoropolymer binder, the second fluoropolymer binder, andthe non fluoropolymer binder in the binder composition was 15:85:0. Itis understood that when a value is listed as zero in a ratio that thenumber zero is being included to indicate that the correspondingcomponent is not present and should not be interpreted to have amathematical meaning. For example, the ratio of 15:85:0 in ComparativeExample 2 indicates the non fluoropolymer binder is not present.

Comparative Example 3

A cathode active material slurry, a cathode, and a lithium battery wereprepared in the same manner as in Example 1, except that a weight ratioof the first fluoropolymer binder, the second fluoropolymer binder, andthe non fluoropolymer binder in the binder composition was 0:85:15. Itis understood that when a value is listed as zero in a ratio that thenumber zero is being included to indicate that the correspondingcomponent is not present and should not be interpreted to have amathematical meaning. For example, the ratio of 0:85:15 in ComparativeExample 3 indicates first fluoropolymer binder is not present.

Evaluation Example 1 Binding Force Evaluation (Peel Test)

Each of the cathode plates manufactured according to Examples 1 to 6 andComparative Examples 1 to 3 was cut to a size of 2.5 cm×10 cm, and thecathode plate was placed on a glass slide in such a way that an activematerial layer faced the glass slide, and then, the cathode plate wasattached to glass slide by using a roller. A part of the cathode plate(i.e., current collector) was separated from the glass slide on which acathode active material layer is attached and then folded in an oppositedirection.

The glass slide on which a cathode active material layer is attached andthe folded part of cathode plate (i.e., folded current collector) wereseparately grabbed by a UTM tester (QC-513A2 of Cometech Co., Ltd.,Taichung City, Taiwan), and the glass slide on which a cathode activematerial layer is attached and the current collector of the cathodeplate were pulled at a speed of 100 mm/sec at an angle of 180 degrees tomeasure binding force.

An average binding force in a section in which pulling force wasmaintained constant was used as a binding force of the cathode.

Test results are shown in Table 1 below.

Evaluation Example 2 Electrode Plate Resistance Evaluation

Each of the cathode plates prepared according to Examples 1 to 6 andComparative Examples 1 to 3 was cut to a size of 36Π. A size of 36Πmeans a circular electrode plate having a diameter of 36 mm. When thecathode plate was brought into contact by using RS1300N (NapsonCorporation, Tokyo, Japan), a surface resistance was measured. Tenseconds after the contact, a resistance value was read. In considerationof a weight and a mixture density of a cathode mixture per unit area ofthe cathode plate, a specific resistance (represented as a specificresistance calculated in consideration of a resistance of an electrodeplate and a thickness factor) was calculated. Test results are shown inTable 1 below.

Evaluation Example 3 Electrode Plate Stiffness Evaluation

Each of the cathode plates according to Examples 1 to 6 and ComparativeExamples 1 to 3 was cut to a size of 10 mm×20 mm, and the cathode platewas placed between two points spaced apart at an interval of 10 mm byusing a three point bending tester (self-manufactured), and a center ofthe cathode plate was pushed by using the other pointer to perform abending test. The evaluation speed was 100 mm/min, and the maximumevaluation value was used as a stiffness value. Test results are shownin Table 1 below as the bending stress.

Evaluation Example 4 Slurry Stability Evaluation

Stability of the cathode active material slurries used in Examples 1 to6 and Comparative Examples 1 to 3 was measured as follows: viscosity ofslurry was measured for 3 days using a viscometer, and when theviscosity of slurry changes 20% or more within 3 days, the slurry wasevaluated as having poor stability.

Test results are shown in Table 1 below.

Evaluation Example 5 Loading Amount (L/L (mg/cm²)) Evaluation

A weight (L/L) of a cathode mixture per unit area of each of the cathodeplates prepared according to Examples 1 to 6 and Comparative Examples 1to 3 was measured as described below. The loading amount refers to aweight of a cathode mixture per unit area.

14Π of a circular electrode plate was cut and a weight of the cathodemixture (a weight of a current collector was subtracted from a totalweight of the cathode plate) was divided by the area of 14Π of theelectrode plate. The 14Π of a circular electrode means a circularelectrode plate having a diameter of 14 mm.

Test results are shown in Table 1 below.

Evaluation Example 6 Mixture Density Evaluation

Mixture density of cathode plates prepared in Examples 1 to 6 andComparative Examples 1 to 3 was measured as follows: the loading amount(L/L) measured according to Evaluation Example 5 was divided by athickness of the cathode mixture (a thickness of a current collector wassubtracted from a thickness of a cathode plate).

Test results are shown in Table 1 below.

Evaluation Example 7 4.3V Cut-Off Charging and Discharging Evaluation

Each of the coin cells manufactured according to Examples 1 to 6 andComparative Examples 1 to 3 was charged with constant-current at atemperature of 25° C. at a rate of 0.05 C until voltage reached 4.3V(vs.Li), and while the voltage was maintained at 4.3V, constant-voltagecharging was performed until the current reached 0.02 C. Then, until thevoltage reached 3.0 V (vs. Li) constant-current discharging wasperformed on the coin cells at a rate of 0.05 C. (Formation process)

A lithium battery that had been subjected to the formation process wascharged with constant-current at a temperature of 25° C. at a rate of0.1 C until voltage reached 4.3V (vs. Li), and then, while the voltagewas maintained at 4.3V, constant-voltage charging was performed untilthe current reached 0.02 C. Then, until the voltage reached 3.0 V (vs.Li), constant-current discharging was performed at a rate of 0.1 C.These charging and discharging processes were repeatedly performed 100times. A capacity retention ratio is represented by Equation 1 below.Charging and discharging test results are shown in Table 1 below.

Capacity retention ratio=[discharge capacity in 100^(th) cycle/dischargecapacity in 1^(st)]×100  Equation 1

Evaluation Example 8 4.4V Cut-Off Charging and Discharging Evaluation

Each of the coin cells manufactured according to Examples 1 to 6 andComparative Examples 1 to 3 was charged with constant-current at atemperature of 25° C. at a rate of 0.05 C until voltage reached 4.4V(vs. Li), and then, while the voltage was maintained at 4.4V,constant-voltage charging was performed until the current reached 0.02C. Then, until the voltage reached 3.0 V (vs. constant-currentdischarging was performed on the coin cells at a rate of 0.05 C.(Formation process)

A lithium battery that had been subjected to the formation process wascharged with constant-current at a temperature of 25° C. at a rate of0.7 C until voltage reached 4.4V (vs. Li), and then, while the voltagewas maintained at 4.4V, constant-voltage charging was performed untilthe current reached 0.02 C. Then, until the voltage reached 3.0 V (vs.Li), constant-current discharging was performed at a rate of 0.5 C.These charging and discharging processes were repeatedly performed 100times. A capacity retention ratio is represented by Equation 1 below.Charging and discharging test results are shown in Table 1 below.

TABLE 1 Electrode Capacity Capacity Binding Bending plate Mixtureretention ratio retention ratio force stress Resistance Slurry L/LDensity [4.3 V cut-off, [4.4 V cut-off, [gf/mm] [mN] [Ω] Stability[mg/cm²] [mg/cm³] at 100 cycle] at 100 cycle] Example 1 1.09 2.74 10.62High 55.0 3.95 92.1 84.6 Example 2 1.13 2.97 10.50 High 55.0 3.96 92.284.4 Example 3 0.99 3.12 10.89 High 55.1 3.95 92.1 83.9 Example 4 1.293.52 11.29 High 55.1 3.95 90.2 83.4 Example 5 1.35 4.17 12.20 High 55.23.94 90.4 83.4 Example 6 1.18 4.25 12.08 High 55.1 3.94 88.1 79.9Comparative 1.12 4.97 15.78 Low 55.0 3.95 81.0 71.9 Example 1Comparative 0.87 1.97 16.30 Low 55.0 3.94 82.0 70.2 Example 2Comparative 1.11 2.21 11.98 High 55.1 3.95 81.7 71.8 Example 3

As shown in Table 1, the cathodes of the lithium batteries manufacturedaccording to Examples 1 to 6 include a binding force and flexibility atthe same time due to the use of a novel binder composition, andaccordingly, compared to the lithium batteries manufactured according toComparative Examples 1 to 3, the lithium batteries have improved energydensity and lifespan characteristics.

Since the lithium battery of Comparative Example 1 had a relatively lowamount of the second fluoropolymer binder, slurry stability thereof wasdecreased; since the lithium battery of Comparative Example 2 did notinclude the non fluoropolymer binder, dispersibility of a conductiveagent was decreased, and accordingly, stability of slurry was decreased;and since the lithium battery of Comparative Example 3 did not includethe first fluoropolymer binder, flexibility of an electrode plate wasdecreased, and thus, an electrode plate (specifically, electrode activematerial layer) was cracked.

Due to the inclusion of a binder composition for a secondary batteryincluding a first fluoropolymer binder including a tetrafluoroethylenepolymer binder, a second fluoropolymer binder including a vinylidenefluoride binder, and a non fluoropolymer binder including a repeatingunit derived from an acryl monomer and a repeating unit derived from anolefin monomer, a lithium battery may have improved energy density andcyclic characteristics.

It should be understood that the exemplary embodiments described thereinshould be considered in a descriptive sense only and not for purposes oflimitation. Descriptions of features or aspects within each embodimentshould typically be considered as available for other similar featuresor aspects in other embodiments.

While one or more embodiments of the present disclosure have beendescribed with reference to the figures, it will be understood by thoseof ordinary skill in the art that various changes in form and detailsmay be made therein without departing from the spirit and scope of thepresent embodiments as defined by the following claims. In the presentdisclosure, the terms “Example,” “Evaluation Example” and “ComparativeExample” are used to identify a particular example or experimentationand should not be interpreted as admission of prior art.

What is claimed is:
 1. A binder composition for a secondary battery, thebinder composition comprising: a first fluoropolymer binder comprising atetrafluoroethylene polymer binder; a second fluoropolymer bindercomprising a vinylidene fluoride binder; and a non fluoropolymer bindercomprising a repeating unit derived from an acryl monomer and arepeating unit derived from an olefin monomer.
 2. The binder compositionof claim 1, wherein the first fluoropolymer binder is a copolymercomprising: a repeating unit derived from a tetrafluoroethylene monomer;and a repeating unit derived from at least one fluorine-containingmonomer selected from the group consisting of vinylidenefluoride,hexafluoropropylene, chloro trifluoroethylene, andperfluoroalkylvinylether.
 3. The binder composition of claim 1, whereinthe first fluoropolymer binder further comprises a polar functionalgroup.
 4. The binder composition of claim 3, wherein the polarfunctional group of the first fluoropolymer binder comprises at leastone selected from the group consisting of a carboxylic acid group, asulfonic acid group, a phosphoric acid group, a hydroxy group, and ananhydride group, or a salt of the group.
 5. The binder composition ofclaim 1, wherein a weight average molecular weight of the firstfluoropolymer binder is 100,000 g/mol or more.
 6. The binder compositionof claim 1, wherein an amount of the first fluoropolymer binder is in arange of about 3 weight % to about 27 weight % based on a total weightof the binder composition.
 7. The binder composition of claim 1, whereinthe second fluoropolymer binder is a vinylidene fluoride binder thatdoes not comprise a polar functional group.
 8. The binder composition ofclaim 1, wherein a weight average molecular weight of the secondfluoropolymer binder is 300,000 g/mol or more.
 9. The binder compositionof claim 1, wherein an amount of the second fluoropolymer binder is in arange of about 46 weight % to about 94 weight % based on a total weightof the binder composition.
 10. The binder composition of claim 1,wherein an amount of a repeating unit derived from an acryl monomer inthe non fluoropolymer binder is in a range of about 1 weight % to about70 weight %.
 11. The binder composition of claim 1, wherein therepeating unit derived from an acryl monomer in the non fluoropolymerbinder comprises a nitrile group.
 12. The binder composition of claim 1,wherein the repeating unit derived from an olefin monomer in the nonfluoropolymer binder comprises a conjugated diene monomer.
 13. Thebinder composition of claim 1, wherein an iodine value of the nonfluoropolymer binder is 100 or less.
 14. The binder composition of claim1, wherein a glass transition temperature of the non fluoropolymerbinder is in a range of −40° C. to 30° C. g/mol or more.
 15. The bindercomposition of claim 1, wherein an amount of the non fluoropolymerbinder is in a range of about 3 weight % to about 27 weight % based on atotal weight of the binder composition.
 16. A cathode comprising: acathode active material; a conductive agent; and the binder compositionof claim
 1. 17. The cathode of claim 16, wherein an amount of the bindercomposition is in a range of about 0.5 to about 5 parts by weight basedon 100 parts by weight of the cathode active material.
 18. The cathodeof claim 16, wherein a weight of a cathode mixture per unit area of thecathode is higher than 54.0 mg/cm².
 19. A lithium battery comprising:the cathode of claim 16; an anode; and a separator.
 20. The lithiumbattery of claim 19, wherein a voltage of the lithium battery is 4.0 Vor more.